This invention relates to apparatus for performing device and failure analysis of microcircuit chips, and in particular to means for detecting and indicating the contact of a microcircuit analyzer probe to metalization and to junctions on chips under test.
Apparatus for performing microcircuit analysis and testing has, in the past, been unreliable and has, in certain instances, caused damage to or has destroyed the device under test. Commonly, the device under test is probed with tungsten probes the output of which is fed to a curve tracer. When contact to metalization that is only a few microns square is required, Kelvin probes are found to be too bulky. Ambiguity in the curve tracer output could therefore result because of the uncertainties as to whether a failure was a failure in the device being tested or a failure of the probe to make proper contacts. Another problem with state-of-the art devices is that of detecting a positive contact to a junction when reverse bias leakage current may be only a few namoamperes. When observing this leakage current on a curve tracer there is no indication that contact has been made until the voltage reaches 15 or 20 volts. If there is poor ohmic contact under these conditions the higher voltage could cause sparking at the probe contact and damage the device being tested.
In essence, therefore, the basic and most pressing problem currently encountered in microcircuit analysis is that of making positive contact to the microcircuit metalization, contact cuts through the oxide junction contacts, or contacts to a diffused resistor with greater ease, with greater reliability and with little chance of damaging the device under test. The present invention is directed toward solving this problem.